This invention relates to olefin polymerization catalysts and particularly relates to specific modifier compounds useful in a supported alpha-olefin polymerization catalyst system.
Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halide-based catalyst components. Also known is incorporating an electron donor compound into the titanium-containing component. An olefin polymerization system typically comprises a titanium-containing compound, an alkylaluminum compound and an electron donor modifier compound. The electron donor modifier used in combination with the alkyl aluminum compound and solid titanium-containing compound is distinct from the electron donor which may be incorporated within the titanium-containing compound. Many classes of electron donors have been disclosed for possible use as electron donor modifiers used during polymerization.
One class of such electron donor compounds is organosilanes. For example in U.S. Pat. No. 4,540,679, organosilanes, especially aromatic silanes are described. Use of organosilanes as cocatalyst modifiers also is described in Published U.K. Application No. 2,111,066 and Published European Application Nos. 86,288, 86,471, 86,472 and 86,473. Other aliphatic and aromatic silanes used in polymerization catalysts are described in U.S. Pat. Nos. 4,420,594, 4,525,555 and 4,565,798. Typically, it has been found that aliphatic silanes are not as effective as aromatic silanes. It has been found that certain aromatic silanes may produce undesirable products. The invention described herein is a species of aliphatic silane which performs better than other aliphatic silanes as an olefin catalyst electron donor modifier and in many instances as well as, or better, than aromatic silanes.